In recent years, as one of causes of a global warming phenomenon, a greenhouse effect due to CO2 has been pointed out, and countermeasures against the effect have also become an internationally urgent need in protecting the global environment. A source of generation of CO2 ranges in various fields of human activities in which fossil fuel is combusted, and a demand for suppressing the discharge tends to be further strengthened. Accordingly, directed at a power generation apparatus such as a thermal power plant that uses a large amount of fossil fuel, a method of removing and recovering CO2 in a flue gas by bringing the flue gas of an industrial apparatus, such as a boiler and a gas turbine, into contact with an amine-based CO2 absorbent, and an air pollution control system that stores the recovered CO2 without releasing it to the atmosphere have been extensively studied.
A CO2 recovery unit having a process of bringing a flue gas and a CO2 absorbent into contact with each other in a CO2 absorber (hereinafter, also simply referred to as “absorber”), and a process of heating the CO2 absorbent that has absorbed CO2 in a CO2 absorbent regenerator (hereinafter, also simply referred to as a “regenerator”), diffusing CO2, regenerating the CO2 absorbent and circulating the absorbent to the CO2 absorber again to reuse the CO2 absorbent, as a process of removing and recovering CO2 from the flue gas using the above-described amine-based CO2 absorbent, has been suggested (for example, see Patent Literature 1).
In the CO2 absorber, the flue gas is brought into countercurrent contact, for example, with the amine-based CO2 absorbent such as alkanolamine, CO2 in the flue gas is absorbed to the CO2 absorbent by a chemical reaction (exothermic reaction), and the flue gas after removal of CO2 is released out of the system. The CO2 absorbent that has absorbed CO2 is also called a rich solution. The rich solution is increased in pressure by a pump, heated in a heat exchanger by the high-temperature CO2 absorbent (lean solution) obtained by diffusion of CO2 and regeneration in the regenerator, and supplied to the regenerator.
In the CO2 recovery process using the CO2 absorbent, the CO2-free flue gas obtained by removing CO2 from the flue gas is released to the atmosphere. However, since a small part of a small amount of amine absorbent is present in the released gas, it is necessary to reduce an amount of discharge thereof.
In particular, in the future, when the CO2 removal regulation is started, there is a possibility that the CO2 removal device itself increases in size, and thus, it is necessary to further reduce the amount of discharge.
As a technique that prevents the release of the amine absorbent, for example, a method of recovering an amine compound accompanied by a CO2-free flue gas, by providing a plurality of stages of water washing sections on a downstream side of a CO2 absorption section of a CO2 absorber of a CO2 removal device, and by bringing the CO2-free flue gas and washing water into vapor-liquid contact with each other has been suggested (Patent Literature 2).
In addition, as another technique, a method of recovering a basic amine compound in a decarbonator flue gas that sprays a sulfuric acid from a sulfuric acid spray device to a CO2-free flue gas discharged from a CO2 absorber, converts an amine absorbent accompanied by the flue gas into a basic amine compound sulfate, and collects the basic amine compound sulfate has been suggested (Patent Literature 3).
Furthermore, in the air pollution control system, when a mist generation material being a generation source of mist generated in the absorber of the CO2 recovery unit is contained in the flue gas introduced into the CO2 absorber that absorbs CO2 in the CO2 recovery unit, the CO2 absorbent is accompanied by the mist generation material. Therefore, there is a problem that the amount of CO2 absorbent that scatters to the outside of the system increases, and thus, the countermeasures against the problem have been considered (Patent Literature 4).